For more than a decade, investing in Latin America was all about Brazil. But it's power is waning, and the bigger opportunities -- and growth drivers -- are in Mexico. Investors should take note.

The Beatles would have been incomplete without either John Lennon or Paul McCartney, but just about everyone has a favorite. The same holds true for Latin America, where Mexico and Brazil vie for the hearts and dollars of investors, and together make up about 80% of the MSCI Latin America Index. While arguing Lennon versus McCartney might make for entertaining conversation, the stakes are higher when it comes to...